To gain insight into the pathogenesis of Duane syndrome (DS), we are investigating its genetic basis. The neuropathologic findings in DS support our hypothesis that it results from aberrant development of abducens motor neurons and/or aberrant axonal targeting of cranial nerve VI with secondary extraocular muscle dysinnervation. In this grant, I seek funding to support my project to positionally clone and identify the gene that is mutated in an autosomal dominant form of Duane syndrome that has been mapped to a genetic locus on chromosome 2 (the DURS2 locus), and to determine if this gene is also mutated in small families and sporadic cases of DS. This work will address the following specific aims: Aim 1: Identify the DURS2 disease gene by analysis of candidate genes within the critical region. Aim 2: Determine if mutations or polymorphisms in the DURS2 gene cause DS in small families and sporadic cases. Aim 3: Determine if we can detect any correlations between DURS2 mutations and specific Duane syndrome phenotypes.